Caption: Cause of sickle cell anaemia, animation. The first frame shows the genetic code (bottom) and amino acid sequence for normal red blood cells along with their structure (top). In the second frame a mutation has changed the DNA (deoxyribonucleic acid) coding the amino acid glutamine (GAG) so that it codes for valine (GUG). This alters the structure of the blood cells, causing them to become crescent shaped.